The invention relates to a device for the heat treatment of a material passing through a plurality of treatment zones. A heated gaseous treatment medium which is conducted substantially in a closed circuit is continuously replenished. A fractional portion flows off by way of a heat exchanger which supplies energy from the portion flowing off to a fresh replacement portion flowing in and added to the closed circuit.
In the case of known heat treatment devices having a plurality of treatment zones, that part or fraction of the treatment medium that is to be carried off is exhausted by way of individual channels, or ducts from the individual treatment zones of the device and is conducted to a central heat exchanger. Downstream from the central heat exchanger there is coupled a ventilator which delivers the spent and cooled treatment medium to the atmosphere. A part or fraction of new replacement medium which corresponds quantitatively to that part of the treatment medium that is carried off and vented, is preheated in a counterflow by way of the central heat exchanger and is supplied once more to the individual treatment zones by way of a fan, or blower as well as individual channels connected thereto.
As a result of the ducting or piping system necessary for this purpose, the known construction is very complicated and expensive. It requires, in addition to the fans which are present in the individual treatment zones for circulation, an additional central fan as well as a framework, suitably dimensioned depending on the particular installation to mount the central fan. Furthermore, a fan or fans, the heat exchanger, and the entire ducting and piping system have to be sealed off carefully, in order to properly separate that portion of the treatment medium that is to be carried off, from that part of the treatment medium that is to be supplied. Otherwise the mode of operation and equilibrium of the heat exchanger is disturbed, and the amount of energy recovered is reduced.
Furthermore, the ducts and pipes have to be well insulated, since their comparatively large overall surface area would, in the event of insufficient insulation, cause correspondingly large heat losses.